Burt Sara A, Ojo-Fakunle Victoria T A, Woertman Jenifer, Veldhuizen Edwin J A
Institute for Risk Assessment Sciences, Veterinary Public Health Division, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
PLoS One. 2014 Apr 1;9(4):e93414. doi: 10.1371/journal.pone.0093414. eCollection 2014.
The formation of biofilm by bacteria confers resistance to biocides and presents problems in medical and veterinary clinical settings. Here we report the effect of carvacrol, one of the major antimicrobial components of oregano oil, on the formation of biofilms and its activity on existing biofilms. Assays were carried out in polystyrene microplates to observe (a) the effect of 0-0.8 mM carvacrol on the formation of biofilms by selected bacterial pathogens over 24 h and (b) the effect of 0-8 mM carvacrol on the stability of pre-formed biofilms. Carvacrol was able to inhibit the formation of biofilms of Chromobacterium violaceum ATCC 12472, Salmonella enterica subsp. Typhimurium DT104, and Staphylococcus aureus 0074, while it showed no effect on formation of Pseudomonas aeruginosa (field isolate) biofilms. This inhibitory effect of carvacrol was observed at sub-lethal concentrations (<0.5 mM) where no effect was seen on total bacterial numbers, indicating that carvacrol's bactericidal effect was not causing the observed inhibition of biofilm formation. In contrast, carvacrol had (up to 8 mM) very little or no activity against existing biofilms of the bacteria described, showing that formation of the biofilm also confers protection against this compound. Since quorum sensing is an essential part of biofilm formation, the effect of carvacrol on quorum sensing of C. violaceum was also studied. Sub-MIC concentrations of carvacrol reduced expression of cviI (a gene coding for the N-acyl-L-homoserine lactone synthase), production of violacein (pigmentation) and chitinase activity (both regulated by quorum sensing) at concentrations coinciding with carvacrol's inhibiting effect on biofilm formation. These results indicate that carvacrol's activity in inhibition of biofilm formation may be related to the disruption of quorum sensing.
细菌形成生物膜会使其对杀菌剂产生抗性，并在医学和兽医临床环境中引发问题。在此，我们报告牛至油的主要抗菌成分之一香芹酚对生物膜形成的影响及其对现有生物膜的活性。实验在聚苯乙烯微孔板中进行，以观察：（a）0 - 0.8 mM香芹酚对选定细菌病原体在24小时内生物膜形成的影响；（b）0 - 8 mM香芹酚对预先形成的生物膜稳定性的影响。香芹酚能够抑制紫色色杆菌ATCC 12472、肠炎沙门氏菌亚种鼠伤寒沙门氏菌DT104和金黄色葡萄球菌0074生物膜的形成，而对铜绿假单胞菌（野外分离株）生物膜的形成没有影响。在亚致死浓度（<0.5 mM）下观察到香芹酚的这种抑制作用，此时对细菌总数没有影响，这表明香芹酚的杀菌作用并非导致观察到的生物膜形成抑制的原因。相比之下，香芹酚（高达8 mM）对所述细菌的现有生物膜几乎没有或没有活性，这表明生物膜的形成也赋予了对该化合物的保护作用。由于群体感应是生物膜形成的重要组成部分，因此还研究了香芹酚对紫色色杆菌群体感应的影响。亚最小抑菌浓度的香芹酚在与香芹酚对生物膜形成抑制作用一致的浓度下，降低了cviI（编码N - 酰基 - L - 高丝氨酸内酯合酶的基因）的表达、紫色菌素（色素沉着）的产生和几丁质酶活性（两者均受群体感应调节）。这些结果表明，香芹酚抑制生物膜形成的活性可能与群体感应的破坏有关。
